Press machines are used to punch or shape material. These press machines are power components which are fitted with dies. One portion of the die is attached to a stationary bed of the machine. The second portion of the die is attached to a slide which reciprocates to open and close the die to perform the desired operation on the material. The portions of the die are closed to shape the material and the die portions are opened to insert and remove the material. Inserting and removing the material can be accomplished by machines or performed manually.
It is desirable to control the press clutch such that the slide will repeatedly stop at the top of the stroke at approximately the same position. As the press brake wears, the stopping time for the slide will increase and the slide will not stop until it is moved past the top of the stroke and begins to move downward toward the work area.
Systems have been heretofore proposed wherein the position of the brake at its stopped position is detected and the distance required for stopping, is measured. Such a system is described in U.S. Pat. No. 3,931,727 issued to Luenser on Jan. 13, 1976 and entitled "Method in a Metal Forming Machine". However, on machines which have a variable speed of operation it is desirable to adjust the point of slide position at which the stopping action is initiated, in order to compensate for the inherent change in stopping distance resulting from the change in speed of operation.
Other related aspects of press machines involve the monitoring of clutch valves. For reliable clutch and brake action, double safety valves are used. The operation of these valves are monitored either pneumatically or electrically. In the operation of clutch valves there should be no significant increase in stopping time resulting from the failure of one section of the valve. It is desirable that when such a failure occurs that the press machine be stopped and prevented from being operated until correction of the clutch valve is made. It is therefore desirable to excercise the valve monitor frequently to determine if the monitor is viable and functional. Further, automatic monitoring is desirable.
It is further desirable to limit the single stroking rate of clutch and brake actuations of press machines to limit brake lining temperatures to preestablished limits.
A need has thus arisen for a press clutch control system having improved reliability aspects. A need has arisen for causing the press slide to stop at the top of the slide's cycle for variable speed presses. A need has further arisen for an improved clutch valve monitor test system as well as a monitoring system for brake operation within the thermal limit of the brake.